1. Field of the Invention
The invention relates to an annular anti-wear shim for a turbomachine, in particular for an annular hook of a turbomachine stator, nozzle, or casing.
2. Description of the Related Art
A guiding stator or nozzle in a turbomachine comprises an annular row of stationary vanes extending radially between an inner annular platform and an outer annular platform, the outer platform having two annular hooks, one upstream and the other downstream, that co-operate with corresponding hooks of a casing or of a shroud carried by the casing of the turbomachine.
In operation, as a result of micromovements generated by vibration and by differential thermal expansion of the parts, the hooks of the stator and of the shroud or casing can become worn by rubbing against each other. In order to remedy the problem of the hooks suffering wear by rubbing, it is known to engage an annular anti-wear shim of channel section on each of the hooks so as to eliminate any direct contact between the hooks. The shim is made of a material that wears more easily in rubbing than the materials of the hooks, and it is intended to be replaced during a maintenance operation once it has becomes too worn.
Applications FR 2 938 872 and FR 10/59696 in the name of the Applicant describe annular anti-wear shims of this type.
In order to optimize the performance of the turbomachine, it is important to provide good radial sealing upstream from the stators of the compressor (or the nozzles of the turbine) between the upstream end of the outer platform of each stator and the facing downstream end of the shroud of the casing situated upstream from the stator. This makes it possible to avoid recirculation upstream from the stator, where such recirculation would reduce the performance and the operability of the turbomachine.
In the prior art, it is known to provide such sealing by having the upstream end of the outer platform of the stator bear axially against the downstream end of the shroud situated upstream, this axial bearing being maintained by an undulating ring that is elastically deformable in the axial direction and that is mounted downstream from the downstream hook of the stator. The ring is mounted with prestress in the axial direction in a housing of the casing or of a shroud and it bears axially against the downstream hook of the stator in order to urge the stator upstream and to keep it bearing in sealed axial manner against the upstream shroud.
However, that technology cannot be used in all engines, in particular in engines of small size, since it is too bulky. This applies in particular when the location in the downstream shroud that is to receive a ring of this type is already occupied by other elements such as vibration dampers.